Problem: Tiffany is 42 years old and Stephanie is 3 years old. How many years will it take until Tiffany is only 4 times as old as Stephanie?
Solution: We can use the given information to write down an equation about how many years it will take. Let $y$ be the number of years that it will take. In $y$ years, Tiffany will be $42 + y$ years old and Stephanie will be $3 + y$ years old. At that time, Tiffany will be 4 times as old as Stephanie. Writing this information as an equation, we get: $42 + y = 4 (3 + y)$ Simplifying the right side of this equation, we get: $42 + y = 12 + 4 y$ Solving for $y$ , we get: $3 y = 30$ $y = 10$.